The invention relates to a substrate for high voltage modules with a reduced electric field strength.
In electronics and electrical engineering, circuits and circuit devices are often built up on boards or insulating material metallized on two sides. For example, in power electronics, ceramic boards coated with copper on both sides are used. The ceramic board thereby constitutes an insulator with a given dielectric constant. The components are mounted on the structured metal layer. In this case, very high electric field strengths occur, in particular at the lateral edges of the upper metal layer, because of the high electrical voltage present between the contact surfaces. For example, the field strength is up to 50 kV/mm at a voltage of 5000 V. At this field strength, because of the breakdown voltage being exceeded at the transition to the ceramic, that is to say to the insulator, the insulation requirements which are placed on power modules can no longer be met or at least can no longer be complied with reliably.
The object of the present invention is to provide a substrate for a high voltage module which overcomes the above-noted deficiencies and disadvantages of the prior art devices and methods of this general kind, and in which, with the same geometry of insulator and metallization, the breakdown voltage is shifted to higher values.
With the above and other objects in view there is provided, in accordance with the invention, a substrate for high voltage modules, comprising:
a ceramic layer having a first main side, a second main side opposite the first main side, and a first dielectric constant ∈1;
an upper metal layer on the first main side and a lower metal layer on the second main side; and
a dielectric layer with a second dielectric constant ∈2 disposed on the first main side adjacent the upper metal layer on the ceramic layer.
In other words, the solution is based on reducing the field strength at the edges of the metallization. To this end, a dielectric layer with a second dielectric constant is provided on the ceramic layer, adjoining the upper metallization. As a result, the maximum field strength at the transition from the substrate (ceramic and metallization) to its surroundings can be reduced substantially.
The advantage of the invention resides in the fact that no significant change has to be made to the basic structure of the components currently used but, with the invention, simple protection can be achieved against peak discharges which would destroy the electronic circuit.
In accordance with an added feature of the invention, the upper metal layer is at least partly embedded in the ceramic layer.
In accordance with an additional feature of the invention, the upper metal layer is connected to the lower metal layer via the dielectric layer. This permits the suppression of the surface discharge at the edge of the metallizations which, at excessively high operating voltages, can lead to destruction of the soft encapsulation.
In a preferred embodiment, the second dielectric constant ∈2xe2x89xa710.
In accordance with a concomitant feature of the invention, the dielectric layer has a thickness approximately equal to a thickness of one of the upper metal layer and the lower metal layer.
Since the dissipation of the field peak depends on the thickness of the dielectric layer, it is advantageous to have the thickness of the dielectric layer approximately assume the thickness of the upper or the lower metal layer. A high dielectric constant also leads to the dissipation of the field peak.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a substrate for high voltage modules, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.